Process for producing voluminous yarn



United States Patent 3,012,396 PROCESS FOR PRODUCING VOLUMINOUS YARN Hans R. Stucki, Summit, N.J., and Herman D. Noether, Kew Gardens, N.Y., assignors to Celanese Corporation of America, New York, N.Y., a corporation of Delaware No Drawing. Filed July 5, 1955, Ser. No. 520,157

. 11 Claims. ((31. 57-157) This invention relates to voluminous yarn and relates more particularly to .an improved process for the production of voluminous yarn of highly substituted organic acid esters of cellulose.

It has previously been proposed to produce a voluminous yarn of highly substituted organic acid esters of cellulose, such as cellulose acetate, by twisting and untwisting the said yarn and treating the said yarn to develop therein a crystalline structure so as to set the crimp therein. The voluminous yarn prepared in this manner will retain a substantial proportion of its crimp during the operations to which it is normally subjected during its conversion into a fabric and also into a final consumer product. As a result, the said yarn is well suited for widespread commercial use.

The voluminous yarn may be prepared on a batch basis, by twisting the yarn and winding the said twisted yarn onto a package, raising the package to an elevated temperature to develop in the yarn the desired'crystalline structure, and finally untwisting the yarn. In the interest of economy, however, it is preferred to operate in a continuous manner by twisting and untwisting the yarn, for example, in a false twist spindle and raising the yarn to an elevated temperature as it passes through a suitable treating apparatus. To obtain a high degree of crimp in the final product, the twist to which the yarn is subjected must be quite high. The insertion of such a high twist into the yarn places a considerable amount of tension on the yarn. When the yarn is treated with a heated fluid under pressure, such as steam, to develop crystallinity therein by passing the said yarn into, through and out of a steam chamber, another source of tension in the yarn arises from the forces exerted thereon by the escape of steam from the entrance and exit orifices through which the yarn enters and leaves the steam chamber. The tension on the yarn, regardless of its source, tends to stretch the yarn, particularly when the voluminizing of the yarn is carried out in a continuous manner. Such stretching tends to reduce the yarn elongation and also to alter its other properties in an unfavorable and irregular manner and may result in a yarn which is not suited for textile processing such as weaving or knitting. It is possible to minimize the stretching of the yarn by holding the tension thereon to a minimum. However, it is not possible to eliminate the tension on the yarn completely. Furthermore, when it is attempted to operate under extremely low yarn tensions, diificulties arise owing to the tendency for the slightest changes in tension to alter the properties of the volumim'zed yarn and to the increased yarn breakage which occurs at such low tensionsbecause of the lack of control of the yarn during its movement through the apparatus.

It is an important object of this invention to provide a process for voluminizing highly substituted organic acid ester of cellulose yarns which will be free from the foregoing and other difiiculties. A further object of this invention is to provide a process for voluminizing highly substituted organic acid ester of cellulose yarns in which the yarn is first pretreated to develop therein a crystalline structure before it is subjected to a voluminizing operation.

Other objects of this invention will be apparent from the following detailed description and claims.

According to the present invention, a highly substituted organic acid ester of cellulose yarn, such as a cellulose acetate yarn, is first pretreated to develop therein a crystalline structure. The so-treated cellulose acetate yarn is then voluminized by twisting and untwisting the same and again treating the same under such conditions as would develop in an untreated yarn a crystalline structure so as to set the crimp therein. When the pretreated yarn is voluminized, there is no tendency for the said yarn to stretch or for other properties of the said yarn to be altered even though the said yarn is subjected to considerable tension during the voluminizing operation. As a result, the product obtained by the process of this invention is found to have a good tenacity and elongation and to be free from other defects which would impair its suitability for commercial textile processing.

The crystalline structure of the yarn can be measured by X-ray diffractometry. The degree of pretreatment or heat treatment of the yarn can be measured by observing arcs of the fiber.

the number and/or the sharpness of the major diffraction Thus, for example, cellulose triacetate has fourpronounced diffraction peaks at 8, 10, 12.6 and 16 29 where 20 is the angle which the diffracted X-ray beam makes with respect to the incoming beam. Depending on the degree of treatment these peaks show differences in intensity, height and width. A quantitative representation of these differences is found by measuring the ratio of peak height to width at half height for a series of diftraction peaks, from X-ray difiractometer curves or microphotometered X-ray photographs. Gne specific measure of the crystalline structure is the crystalline order index. It represents the average of the ratios of each peak height to its width at half height of the four diffraction peaks at 8, 10, 12.6 and 16 26.

The pretreatment of the cellulose acetate yarn to develop therein the crystalline structure may be carried out in any desired manner. For example, bobbins, cones or other packages of the said yarn may be r'aised to an elevated temperature by treatment with stream, water, heated air, or the like. It is preferred to use stream under superatmospheric pressure for this purpose because of the rapid and efiicient transfer of heat to the yarn that While the original untreated yarn would show only 2 diffuse .during the twisting and untwisting operations toset the crimp therein. lhe pretreatment of the yarn in accordthis makes possible. Another way in which the pretreatment of the yarn can be carried out is to pass the yarn continuously through a treating zone where'it is raised to an elevated temperature in any desired manner. Since, during this pretreatment, there is no need to twist or untwist the yarn, it is possible to carry out the pretreatmeat with the yarn in a substantially tensionless condition so that no stretching of the yarn will take place. The crystalline structure developed in the yarn during the pretreatment should be such that its crystalline order in dex measured as described above is at least 1.2 and preferably 1.3 to.l.5 An X-ray photograph of such a yarn would show four weak but distinct diffraction arcs at 8, 10, 12.6 and 16 26 in the case of cellulose triace tme,

broad arcs or diffraction rings.

After the yarn has been pretreated in the manner specified above, it is subjected to a voluminizing operation by twisting and untwisting the same and treating the yarn under conditions that would develop in an untreated yarn .a crystalline structure so as to set the crimp therein. The

voluminizing operation may be carried out on a batch basis by twisting the yarn and winding the twisted yarn onto a package, treating the yarn to set the crimp therein, and unwinding and untwisting the yarn. It is,. however,

preferred to carry out the voluminizing operation in' a continuous manner by twisting and 'untwisting the yarn for example, in a false twist spindle and treating the yarn carry out the process of this invention.

in the cellulose molecule.

ance with this invention is especially useful when the voluminizing is carried out in such a manner, since the yarnis normally subjected to substantial tension during a continuous voluminizing operation. The nature and extent of the treatment of the yarn'during the voluminizing operation should be such that when an untreated yarn is treated under the same conditions it will develop a crystalline structure corresponding to a crystalline order index of at least 1.4 and preferably of 1.7 or higher. 7

To develop the requisite crystalline order index in the yarn during the voluminizing operation, the yarn may be heated to an elevated temperature with hot air, radiant heat, or the like. The best results are obtained when the heating of the yarn is carried out with steam under superatmospheric pressure. The use of steam insures a a thorough and rapid heating of the yarn being treated so that the period of heating may be kept to a minimum.

The extent of the treatment during the pretreatment step to develop in the yarn a crystalline structure may be equal to, greater than or less than the extent of the treatment of the yarn during the voluminizing step. However; it is preferred that the extent of the treatment during'the pretreatment should at most equal the extent of the treatment during voluminizing. If a greater degree of treatment is imparted to the yarn during the pretreatment, difiicul-ties'are encountered in inserting a suihciently high twist into the yarn without imposing excessive tensionson the yarn and possibly damaging the same.

In carrying out the volumiuizing of the yarn, the degree of twist imparted to the yarn should correspond to a twist multiplier of at least about 400, or preferably between about 600 and 700. The twist multiplier is equal to the twist in turns per inch multiplied by the square root of the denier. In general, under the same treatment conditions, the greater the twist, the greater will be the crimping and voluminosity' of the final product.

Any suitable form of apparatus may be employed to A particularly valuable form of such apparatus is shown in Stoll et al. application S. No. 376,434, filed August 25, 1953, wherein the yarn is drawn from a supply package, passed through the heating chamber and then through a false-twist spindle, and finally, after being permitted to relax to a controlled degree, taken up in package form.

The organic acid ester of cellulose yarn to which theprocess of this invention is applicable is that which can be made to develop a crystalline structure. This includes organic acid ester of cellulose yarn having fewer than about 0.5 hydroxyl group, or preferably fewer than about 0.25 free hydroxyl group, per anhydroglucose unit tate, this cor-responds to an acetyl value of at least about 57% or preferably at least about 60%, when calculated as acetic acid. In addition to cellulose acetate,'other organic acid esters of cellulose to which the processof this invention is applicable are cellulose propionate, cellulose butyrate, cellulose acetate formate, cellulose acetate propionate and cellulose acetate hutyrate.

The following example is given to illustrate this'invention further.

Example In the case of cellulose ace A one pound package of 150 denier, 40 filament continuous filament yarn of cellulose acetate having an acetyl value of at least about 60, calculated as acetic acid,

is autoclaved with saturated steam at 20fpounds pressure for 15 minutes. The said yarnfhas then a crystalline 7 order index of 1.3. Thereafter, the pretreated yarn is drawn from the package at the rate of 28 yards per minute-passed through a gate which develops. therein a tensionof 1.5 grams and into a steam chamber where it is exposed to saturated steam at a superatmospheric pressure of 65 pounds per square inch for 0.4 second. The yarn is then passed through a false twist spindle which will twist the yarn between the gate and thespindle to 55 t.p.-i. and immediately untwist the yarn after 'the spindle. Finally, the yarn is taken up in package form. The yarn has a permanent crimp therein and, on measurement, shows a tenacity of 1.1 grams per denier and an elongation of 20 percent. The volumim'zed yarn has a crystalline order index of 1.8. t

It is to be understood that the foregoing detailed description is merely given by way of illustrationand that many variations may be made therein withoutdeparting from the spirit of our invention.

Having described our invention, what we desire to secure by Letterslatent is:

1. Process for voluminizing organic acid ester of cellu lose yarn containing fewer than about 0.25 free hydroxyl group per anhydroglucose unit in the cellulose molecule, which comprises pret-reating the yarn to. develop therein crystaliinity, crimping said yarn by subsequently twisting and untwisting the pretreated yarn under tension, and treating the yarn While at least partially twisted under such conditions as would develop in' an untreated yarn a crystalline structure.

2. Process for voluminizing organic acid ester of cellulose yarn containin'g'fewer than about 0.25 free hydroxyl group per anhydroglucose unit in the cellulose molecule, which comprises pretreating the yarn at an elevated temperature to develop therein crystaliinity, crimping said yarn by subsequently continuously twisting and untwisting the'pretreated yarn under tension, and continuously heating the yarn while at least partially twisted under such conditions as would develop in an untreated yarn a crystalline structure.

3. Process for voluminizing organic acid ester of cellulose yarn containing fewer than about 0.25 free hydroxyl group per anhydroglucose unit in the cellulose molecule, which comprises pretreating the yarn at an elevated tem perature to develop therein crystallinity, crimping said yarn by subsequently continuously twisting and untwisting the pretreated yarn under tension, and continuously heating the yarn while at least partially twisted under such conditions as would develop in an untreated yarn a crystalline structure, the extent of treatment of the yarn during the pretreatment to develop crystallinity being at most equal to the extent of treatment of the yarn while at least partially twisted.

4. Process for voluminiziug org'anicacid ester of cellulose yarn containing fewer than about 0.25 .free hydroxyl group per anhydroglucose unit in the cellulose molecule, which comprises pretreating the yarn at an elevated temperature to develop therein crystallinity such that the crystalline order index is at least 1.2, subsequently crimping the pretreated yarn under tension, and heating the yarn during the crimping under such conditions as would develop in an untreated yarn a crystallinity such that the crystalline order index is at least 1.4.

5. Process for voluminizing cellulose acetate yarn containing fewer than about 0.25 free hydroxyl group per anhydroglucose unit in the cellulose molecule, which comprises pretreating the yarn to develop therein crystallinity, crimping the pretreated yarn under tension, and setting said crimp by treating the yarn under such conditions as would develop crystallinity in an untreated yarn.

6. Process for voluminizing cellulose acetate yarn containing fewer than about 6.25 free hydroxyl group per anhydroglucose unit in the cellulose molecule, which comprises pretreatingthe yarnby heating to develop therein crystallinity, crimping said yarn by subsequently twisting and untwisting'the pretreated-yarn under tension, and heating the yarn while at least partially twisted under ing the pretreated yarn under tension, and heating the yarn while at least part ally twisted under such conditions as would develop crystallinity in an untreated yarn the crystalline order index being at least 1.4.

8. Process for voluminizing cellulose acetate yarn containing fewer than about 0.25 free hydroxyl group per anhydroglucose unit in the cellulose molecule, which comprises pretreating the yarn by heating to develop therein crystallinity such that the crystalline order index is at least 1.2, crimping said yarn by twisting and untwisting the pretreated yarn under tension, and heating the yarn while at least partially twisted under such conditions as would develop crystallinity in an untreated yarn such that the crystalline order index is at least 1.4, the extent of treatment of the yarn during the pretreatment to develop crystallinity being at most equal to the extent of the treatment of the yarn while at least partially twisted.

9. Process for voluminizing cellulose acetate yarn containing fewer than about 0.25 free hydroxyl group per anhydroglucose unit in the cellulose molecule, which comprises pretreating the yarn by heating with steam under superatmospheric pressure to develop therein crystallinity, crimping said yarn by subsequently twisting and nntwisting the pretreated yarn under tension, and heating the yarn with steam under superatmospheric pressure and while it is at least partially twisted under such conditions as would develop crystallinity in an untreated yarn.

10. Process for voluminizing cellulose acetate yarn containing fewer than about 0.25 free hydroxyl group per anhydroglucose unit in the cellulose molecule, which comprises pretreating the yarn by heating with steam under superatmospheric pressure to develop therein crystallinity, such that the crystalline order index is between 1.3 to 1.5, crimping said yarn by continuously twisting and untwisting the pretreated yarn under tension, and heating the yarn with steam under super-atmospheric pressure and while it is at least partially twisted under such conditions as would develop crystallinity in an untreated yarn, such that the crystalline order index is at least 1.7, the extent of treatment of the yarn during the pretreatment to develop crystallinity being at most equal to the extent of the treatment of the yarn while at least partially twisted.

11. In a process of voluminizing including the steps of crimping under tension an organic acid ester of cellulose yarn containing fewer than about 0.25 free hydroxyl group per anh droglucose unit in the cellulose molecule and setting the crimp by developing crystallinity in the yarn, the improvement comprising pretreating the yarn prior to crimping to develop crystallinity therein.

2,089,198 Finlayson et al. Aug. 10, 1937 2,089,778 Whitehead Aug. 10, 1937 2,092,477 Scott et al Sept. 7, 1937 2,198,660 Dreyfus Apr. 30, 1940 2,255,766 Dreyfus Sept. 16, 1941 2,411,429 Hegan et al. Nov. 19, 1946 2,473,615 Sowter June 21, 1949 2,768,870 Drisch et a1 Oct. 30, 1956 2,775,529 Bates et al. Dec. 25, 1956 2,869,318 Stucki Jan. 20, 1959 FOREIGN PATENTS 424,880 Great Britain Mar. 4, 1935 438,589 Great Britain Nov. 13, 1935 

1. A PROCESS FOR VOLUMINIZING ORGANIC ACID ESTER OF CELLULOSE YARN CONTAINING FEWER THAN ABOUT 0.25 FREE HYDROXYL GROUP PER ANHYDROGLUCOSE UNIT IN THE CELLULOSE MOLECULE, WHICH COMPRISES PRETREATING THE YARN TO DEVELOP THEREIN CRYSTALLINITY, CRIMPING SAID YARN BY SUBSEQUENTLY TWISTING AND UNTWISTING THE PRETREATED YARN UNDER TENSION, AND TREATING THE YARN WHILE AT LEAST PARTIALLY TWISTED UNDER SUCH CONDITIONS AS WOULD DEVELOP IN AN UNTREATED YARN A CRYSTALLINE STRUCTURE. 